A randomized clinical trial comparing two alternate methods of provision of warmth to low birth weight (LBW) newborns was undertaken in a referral hospital in Addis Ababa, Ethiopia. The standard, convectively heated infant incubator (INC) is the accepted method of thermal protection of the LBW and sick newborns. Because INC care requires high technology, the acquisition and implementation of this method is beyond the resources of many developing countries. Until recently the only alternative method of provision of warmth to LBW newborns has been the space heated room (SHR) to an average temperature of 30 degrees C. The SHR has been an unsatisfactory alternative because the climatic conditions cannot be individualized to meet the thermal needs of LBW newborns of varying sizes and maturity, and the high environmental temperature required is too uncomfortable for care providers. In response a thermostatically heated, water-filled mattress (HWM) was developed. Since newborns cared for on the HWM are covered, there is less of a need to regulate the thermal environment within a narrow range as naked newborns in INCs. On the other hand, unlike the situation in SHR, the HWM provides a thermal environment that can be adjusted to suit the individual thermal needs of the newborn. Analysis of the results of the randomized trial showed that care in the SHR produced clinically significant cold stress and significant risk of hyperthermia and hypothermia from overheating or inadequate heating. The HWM, on the other hand, was not associated with clinically significant cold stress or risk of inadequate heating or overheating and thus may constitute a feasible and clinically acceptable alternative in providing warmth to LBW newborns during the neonatal period.